Quote:
Originally Posted by Electronic M
Retrovert. I don't think you properly grasp how the circuit or ratings work.
The voltage rating of a resistor only matters for the voltage drop across it, and the voltage between the leads and anything else in close proximity to the case.
The voltage drop across the resistor will normally be well below 500V. A typical color CRT firing 3 guns into a shadow mask that blocks %80 of emissions from reaching the phosphor (thus requiring that much more current for a given brightness) draws around 1mA of current. This 12LP4 Black and White CRT in the original posters set has 1/3 the number of guns and no shadow mask so HV current is likely under 100uA....But let's say he wants to REALLY crank the brightness and draw 500uA HV current to give a worst case normal opperation scenario...500uA through a 680K resistor yields (by ohm's law) a 340V drop across that resistor...That's well below the 500V max rating you quoted for average carbon film resistors.
The case is never kept anywhere near ground (only insulators and other conductors at the same 11KV voltage it's leads are connected to.
Normal carbon film resistors are well within their voltage specs in this application in normal opperation.
The only way their specs would be exceeded would be if HV were shorted to ground (a fault condition). The original resistors had a similar rating to the new carbon film parts, and we're meant to burn up and or arc if HV shorts the same way the modern ones will if you short it out.
The way I see it the new parts will be equivalent for the application.
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exactly!
thus the reason I said it was in there as a safety device to protect against shorting the anode to ground, to do as Retrovert said an use a higher rated volt resister would defeat that feature.
think of it a fusistor!